Soft-magnetic materials used for various reactors, choke coils, pulse power magnetic devices, transformers, antennas, cores of motors, power generators, etc., current sensors, magnetic sensors, electromagnetic wave-absorbing sheets, etc. include silicon steel, ferrite, Co-based, amorphous, soft-magnetic alloys, Fe-based, amorphous, soft-magnetic alloys and Fe-based, fine-crystalline, soft-magnetic alloys. Though silicon steel is inexpensive and has a high magnetic flux density, it suffers large loss at high frequencies, and is difficult to be made thin. Because ferrite has a low saturation magnetic flux density, it is easily saturated magnetically in high-power applications with large operation magnetic flux densities. Because the Co-based, amorphous, soft-magnetic alloys are expensive and have as low saturation magnetic flux densities as 1 T or less, parts made of them for high-power applications are inevitably large, and their loss increases with time due to thermal instability. The Fe-based, amorphous, soft-magnetic alloys have still as low saturation magnetic flux densities as about 1.5 T, and their coercivity is not sufficiently low. The Fe-based, fine-crystalline, soft-magnetic alloys have higher saturation magnetic flux densities and lower coercivity than those of these soft-magnetic materials.
WO 2007/032531 discloses one example of such Fe-based, fine-crystalline, soft-magnetic alloys. This Fe-based, fine-crystalline, soft-magnetic alloy has a composition represented by the general formula of Fe100-x-y-zCuxByXz, wherein X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are numbers (atomic %) meeting the conditions of 0.1≦x≦3, 10≦y≦20, 0<z≦10, and 10<y+z≦24, and a structure in which 30% or more by volume of crystal grains having diameters of 60 nm or less are dispersed in an amorphous matrix, thereby having as high a saturation magnetic flux density as 1.7 T or more and low coercivity. This Fe-based, fine-crystalline, soft-magnetic alloy is produced by quenching an Fe-based alloy melt to form an ultrafine-crystalline alloy ribbon comprising fine crystal grains having an average grain size of 30 nm or less dispersed at a ratio of less than 30% by volume in an amorphous phase, and subjecting this ultrafine-crystalline alloy ribbon to a high-temperature, short-time heat treatment or a low-temperature, long-time heat treatment. The first produced ultrafine-crystalline alloy ribbon has ultrafine crystal grains acting as nuclei for a fine-crystalline structure of an Fe-based, fine-crystalline, soft-magnetic alloy, thereby having low toughness and being difficult to handle.
Amorphous alloy ribbons are generally produced by a liquid-quenching method using a single-roll apparatus, and the ribbon solidified by quenching is continuously wound as it is by a winding apparatus. Winding methods include, for example, a method of adhering the ribbon stripped from a roll to a winding reel with an adhesive tape, and then winding it, as described in JP 2001-191151 A.
Investigation on the stable mass production of the ultrafine-crystalline alloy ribbon of WO 2007/032531 has revealed that it suffers a problem which would not be encountered in the production of conventional amorphous alloy ribbons, namely, a problem of fracture occurring when the ribbon is wound. In the production of an ultrafine-crystalline alloy ribbon, the ultrafine-crystalline alloy ribbon is stripped from a cooling roll by blowing an inert gas (nitrogen, etc.) into a gap between the quenched ultrafine-crystalline alloy ribbon and the cooling roll, and an end of the ultrafine-crystalline alloy ribbon flying in the air is wound around a rotating reel. However, because an object wound by the conventional method is an amorphous alloy ribbon having high toughness and so resistant to fracture, the conventional method is not suitable for winding an ultrafine-crystalline alloy ribbon easily broken because of low toughness. Particularly, when the ribbon is fixed with an adhesive tape as described in JP 2001-191151 A, the ribbon should have excellent twisting stress resistance and shock resistance, because the ribbon flying from a cooling roll is wound around a rotating reel at as high a speed as 30 m/s. However, when stress such as shock is applied to an ultrafine-crystalline alloy ribbon in which large numbers of ultrafine crystal grains are precipitated, the ultrafine crystal grains likely act as stress-concentrated sites, causing fracture. Thus, the ultrafine-crystalline alloy ribbon, to which the present invention is applicable, is easily broken because of low toughness, suffering poor windability.
WO 2011/122589 discloses a primary ultrafine-crystalline alloy having a composition represented by the general formula of Fe100-x-y-zAxByXz, wherein A is Cu and/or Au, X is at least one element selected from the group consisting of Si, S, C, P, Al, Ge, Ga and Be, and x, y and z are respectively numbers (atomic %) meeting the conditions of 0<x≦5, 10≦y≦22, 0≦z≦10, and x+y+z≦25, and a structure in which primary ultrafine crystal grains having an average grain size of 30 nm or less are dispersed at a ratio of 5-30% by volume in an amorphous matrix, its differential scanning calorimetry (DSC) curve having a first exothermic peak and a second exothermic peak smaller than the first exothermic peak between a crystallization start temperature TX1 and a compound-precipitating temperature TX3, and the calorific value of the second exothermic peak being 3% or less of the total calorific value of the first and second exothermic peaks. In WO 2011/122589, however, the fracture of the primary ultrafine-crystalline alloy ribbon at the start of winding is not considered.